The real reason why CVS Health wants Aetna is to expand its vertically-integrated business model. Vertical integration means that one company controls as much of the production, financing, marketing, and distribution of a product or service as possible.

CVS Health is already partially vertically-integrated because it operates both drugstores and prescription-management plans. CVS operates clinics in some of its stores for the exact same reason. Buying a health insurance company would give CVS, even more, control over the process.